1. Field of the Invention
The present invention relates to a shift device with a synchronizer for a transmission of a motor vehicle and the like in which press force applied to a sleeve can be transmitted to a synchronizer ring under a leverage operation using lever members while gears of the transmission are shifted.
2. Description of the Related Art
Such a conventional shift device is disclosed in Japanese Patent No. 3,699,775. This conventional shift device is equipped with a plurality of lever members located among a hub, a sleeve, and a synchronizer ring, where the synchronizer ring is capable of being pressed toward the speed gear due to a leverage operation using the lever members. In addition, the lever members decrease gear noise in a reverse-shift operation in a 5-speed forward transmission.
In any case of synchronization operations toward 5-speed and the reverse-speed, the lever members are pressed and moved toward outwardly in a radial direction due to friction torque generated between friction surface of the synchronizer ring and cone surface of the speed gear to be meshed so as to prevent the sleeve from advancing toward the speed gear until the end of the synchronization operation.
When the synchronization operation ends, force, which is generated due to the friction torque between the synchronizer ring and the speed gear to prevent advance of the sleeve, becomes zero because the friction torque vanishes. Then, the sleeve becomes to be capable of moving toward the speed gear, so that the sleeve advances, pressing the lever members toward inwardly in the radial direction through slanted surfaces formed on inner splines of the lever members. Then the sleeve engages with the speed gear through splines of the sleeve and the speed gear. This is the end of the shift operation.
However, in the above known conventional shift device, there is a problem in that an actual lever ratio of the leverage operation using the lever members cannot be sufficiently obtained because of press force acting on the lever members from the synchronizer ring due to the friction moment generated during the synchronization operation. Therefore, the synchronization performance cannot be sufficiently improved.
The reason will be explained below with reference to drawings of FIGS. 21 and 22 showing cross sectional views of main parts of conventional shift devices. In these figures, configurations of lever members are partially different from those of the above-mentioned prior art, but the operations and effects thereof are essentially the same.
FIG. 21 shows an upper half of a conventional shift device with a synchronizer using a plurality of lever members (In this case, two lever members). The sleeve 20 acts a not-shown force F1 on top portions 24c of the lever members 24 toward a right side in an axial direction in FIG. 20 at contact points W of the sleeve 20 and the lever members 24. The contact points W function as the points of effort in leverage operation using the lever members 24 during the synchronization operation.
The lever members 24 amplify the force F1 into not-shown force F2 due to the leverage operation, and the force F2 acts on the synchronizer ring 22 toward a right side in FIG. 20 at the contact points Y of the lever members 24 and the synchronizer ring 22. The contact points Y function as the points of action. The synchronizer ring 22 is pressed on a friction surface of a not-shown speed gear to perform the synchronization operation. In the leverage operation, contact points X of the lever members 24 and the hub 12 function as the points of support.
In the synchronization operation, projections 22c of the synchronizer ring 22 act not-shown force F3 on the lever members 24 toward outwardly in the radial direction at contact points Z of the projections 22c and the lever members 24. The force F3 is obtained due to the friction torque generated between the friction surface of the synchronizer ring 22 and the cone surface of the speed gear.
Accordingly, a relationship among the forces F1, F2 and F3 becomes below.
The lever ratio of the lever members 24 becomes L2/L1, where L1 is a distance between the point X of the support and the point Y of action, and L2 is a distance between the point X of support and the point W of effort. The lever ratio is, however, actually decreased because of the moment due to the force F3 acting in a direction opposite to a moment obtained due to the force F1 in the leverage operation, because the lever members 24 are inclined in a clockwise direction in FIG. 20 in the synchronization operation, so that speed-gear side edge portions of end portions of the lever members 24 are contacted with the projections 22c at the points Z, that is, at positions a-length L3 apart from the point X toward the synchronizer ring 22 in the axial direction. The length L3 is approximately the same as a thickness of the lever member 4.
Therefore, actual force F2 that presses the synchronizer ring 22 at the points Y toward the right side in the axial direction is expressed as follows.F2=F1·L2/L1−F3·L3/L1
The synchronization performance is decreased because of the existence of F3·L3/L1, where L3 is not a negligible value because it has a length almost the same thickness of the lever member 24
FIG. 22 shows an upper half of a main part of another conventional shift device for obtaining a fifth speed and reverse speed used in a forward five-speed transmission. A sleeve 20 can be meshed with clutch teeth of a not-shown fifth-speed gear when it is moved toward a right side in FIG. 22, while it can be meshed with a not-shown reverse gear when it is moved toward a left side in FIG. 22.
When the sleeve 20 is moved and pushes lever member 24 (In this case, two lever members) toward the left side in FIG. 22, not-shown force F1 acts from the sleeve 20 to the lever members 24 at contact points W thereof, which function as the point of effort during a synchronization operation to press the lever member 24 toward the left side. The lever members 24 turn in a counterclockwise direction around contact points V of the lever members 24 and edge of the hub 12, where the contact points V function as the supporting points in the leverage operation. The lever members 24 act force F2 on the synchronizer ring 22 toward the right side in the axial direction in FIG. 22 at contact points U of the lever members 24 and the synchronizer ring 22.
Thus, the synchronizer ring 22 is pressed on a friction surface of the fifth-speed gear to perform the synchronization operation. This decreases rotational speed of a shaft freely supporting the fifth-speed gear that is held because a vehicle stops. Accordingly, a gear noise is avoided when the sleeve 20 meshes with a not-shown reverse gear.
In this operation, projections 22c of the synchronizer ring 22 contact with and act force F3 on the lever members 24 outwardly in a radial direction at points Z due to friction torque generated between not-shown friction surfaces of the synchronizer ring 22 and the fifth-speed gear.
A relationship among the forces F1, F2 and F3 becomes as follows.F2=F1·L2′/L1′+F3·L3′/L1′where L1′ is a length between the point V of the support and the point U of action, L2′ is a distance between the point V of support and the point U of effort, and L3′ is a length between the point V of the support and the point Z of the projection 22c and the lever member 24.
L3′ is very small, so that an addition F3·L3′/L1′ of the force F2 is also small. Thus, its synchronization performance cannot be sufficiently increased.
It is, therefore, an object of the present invention to provide a shift device with a synchronizer which overcomes the foregoing drawbacks and can improve the synchronization performance.